Certain types of prior personal computer systems include a microprocessor (also referred to as a central processing unit) that is coupled to several types of storage systems--namely, a read only memory ("ROM"), a random access memory ("RAM"), a hard (i.e., fixed) disk drive for mass storage, and a floppy disk drive or drives for storage on removable magnetic floppy disks. The floppy disks are also referred to as diskettes. Those prior personal computer systems typically have an architecture that is especially geared to the storage systems that form a part of each of those prior personal computer systems.
A ROM in conjunction with a program called a ROM monitor stored in the ROM is referred to as firmware. A ROM basic input/output system ("BIOS") module is one type of ROM monitor that is stored in the ROM and used by the operating system for certain personal computers. The ROM BIOS module typically contains (1) drivers for certain hardware, including the keyboard, the disk drives, and the printer; (2) a power-on self-test program ("POST"); (3) a start-up routine that initializes the system; and (4) a loader program that reads the boot or first sector from a diskette or a hard disk.
After the personal computer is turned on, the POST program of the BIOS module is executed, the BIOS start-up routine performs certain initializations, and the loader program reads the contents of the boot sector from a diskette or from a hard disk. That boot sector contains a loader program of the operating system of the computer. That loader program of the operating system in turn loads part of the operating system from a diskette or a hard disk into RAM.
The operating system for the personal computer processes commands, Controls program execution, and oversees the hardware and software resources of the computer system. One type of prior art operating system is MS-DOS sold by Microsoft Corporation of Redmond, Wash. The MS-DOS operating system includes the loader program discussed above, the MS-DOS BIOS, an MS-DOS kernel, a user interface, and utility programs.
The MS-DOS BIOS includes (1) new drivers that extend and use components of the drivers of the ROM BIOS; (2) an initialization routine for the MS-DOS BIOS drivers; and (3) another loader program.
The new drivers of the MS-DOS BIOS are also referred to as BIOS extensions or BIOS ROM extensions. In certain prior art personal computers, all input and output functions are driven by software contained in a 32 kilobyte or 64 kilobyte section of ROM and by smaller (typically 2 kilobyte) BIOS ROM extensions.
The initialization routine for the MS-DOS BIOS drivers displays a copyright notice and adjusts the interrupt table for the new drivers.
The loader program of the MS-DOS BIOS loads the rest of the operating system.
The MS-DOS kernel is a shell between the BIOS and the application program. The MS-DOS kernel initiates application program execution, allocates memory for the application programs, provides an application program interface between the application program and the hardware, and manages the reading and writing of the files.
The user interface of MS-DOS provides information to the user. The user interface provides a prompt, which prompts the user to enter commands. The user interface acts as the manager of the system when the operating system is in control.
The utility programs of MS-DOS provide certain useful functions for MS-DOS. Those functions include (1) formatting a diskette or a hard disk and (2) checking a diskette or a hard disk.
The hard disk and diskettes used with the above-referenced personal computer system are non-volatile storage systems, which means that data is not lost when the power to the computer is turned off. The hard disk and diskettes are types of block storage devices, which means that data is transferred to and from them in blocks.
On the hard disk and on the diskettes, data is physically stored on concentric tracks. Each track is made up of a plurality of sectors. A sector is typically fixed at 512 bytes in length. A disk controller and a physical device driver of a personal computer system typically always write to and read from disks in sector entities.
A cluster is the smallest logically addressable storage unit. For some hard disks, there are four sectors per cluster. For some other hard disks and for a high density 3.5 inch diskette, a cluster is a single sector.
Each partitioned area of a hard disk forms a logical subsystem that can contain its own operating system. A partition table in the first sector of a formatted hard disk contains information about the partitions.
A hard disk and a diskette are formatted before first being used. Low-level formatting divides each track into sectors and places identification ("ID") sector headers at uniform positions around the track. A high-level formatting establishes the clusters, initializes some disk areas, and prepares the disk for receiving data.
At the device driver and the BIOS level, disk requests are described by a "tuple" that indicates the drive, the head, the cylinder/track, the sector, and the length. The logical sector numbers are known at the DOS level and BiOS level. DOS reads and writes to disks in cluster entities.
FIG. 1 shows the logical organization of a prior art MS-DOS operating system. For the MS-DOS operating system, a disk 2 is divided into two logical areas: a system area 4 and a data area 9. The system area contains a boot record 3, a file allocation table ("FAT") 5, and a root directory 7 that contains the root directory entries. The data area 9 contains files that are used to store application programs, data, and subdirectory information.
The boot record 3 includes a bootstrap loader program for loading the operating system. The boot record 3 also includes information as to the ASCII name of the formatting DOS, the number of bytes per sector of the disk, the number of sectors per cluster, the number of sectors in the boot record, the number of copies of the file allocation table, the number of root directory entries, the number of sectors per partition, the disk type number, the number of sectors per file allocation table entry (or cluster), the number of sectors per track, the number of sides per disk, the number of reserved or hidden sectors, the physical drive number, an extended boot sector signature, a volume identification, and a volume table.
The root directory 7 is a table of 32-byte entries that each set forth certain attributes of the file. Typically, each directory entry making up the root directory 7 includes a file name, a file extension, attribute flags, time and date stamps for the file, the starting cluster number for the clusters that make up the file, and the file size.
Each file on the disk is made up of one or more clusters. The file allocation table 5 contains a record in the form of a chain of how the clusters making up the file are linked together. A typical FAT 5 contains a list of two-byte entries, one for each cluster. For some prior FATs, the FAT entries are longer than two bytes. The length of each FAT entry depends upon the total number of clusters. The directory entry for a file contains the starting cluster number for the file, and the operating system uses that starting cluster number to access the file allocation table. Each FAT entry is a pointer to the next cluster of the file. Thus, the FAT entry retrieved by that first access contains the cluster number of the next cluster making up the file. The operating system uses that next cluster number to access the FAT to retrieve yet another cluster number, and continues this process until a special marker in FAT 5 is reached.
The file structure on the disk is tree-like. Entries in the root directory can be pointers to subdirectories. The subdirectories can be nested.
One disadvantage associated with the use of hard disks and diskettes in certain types of prior personal computers is that hard disk drives and floppy disk drives are relatively physically large,.devices with a number of mechanical components. Such large sizes contrast with the small size of integrated circuits that make up many other parts of a personal computer. Moreover, the relatively large size of typical prior hard disk drives and floppy disk drives hinders portable personal computers from being even smaller and more portable.
Another disadvantage associated with prior hard disk drives and floppy disk drives is that they consume a relatively large amount of power compared with the integrated circuits making up other parts of the personal computer.
A further disadvantage associated with the prior hard disk drives and floppy disk drives is that they are prone to failure if exposed to excessive shock and vibration or to dust or other atmospheric contaminants.
Another type of prior non-volatile computer memory is the flash electrically erasable programmable read-only memory ("flash EEPROM"). The flash EEPROM can be programmed by the user, and once programmed, the flash EEPROM retains its data until erased. Electrical erasure of the flash EEPROM erases the entire contents of the memory of the device in one relatively rapid operation. The flash EEPROM may then be programmed with new code.
One disadvantage of one type of prior flash EEPROM, however, is that each single bit cell cannot be overwritten from a logical zero to a logical one without a prior erasure. Another disadvantage of one prior type of flash EEPROM is that it must be erased--i.e., reset to a logical one state--in large blocks or in a manner that erases the entire device.
Another disadvantage of one prior type of flash EEPROM is that there is a finite limit on the number of erase and write cycles for the flash EEPROM before the flash EEPROM will fail.
The limitations with respect to overwriting and erasure associated with certain prior flash EEPROMs have, in certain instances, limited the usefulness of flash EEPROMs in personal computer systems.